At constant speed, the power delivered by the Diesel engine and as would be made available at the terminals of an ideal main generator could be plotted in rectangular coordinates of voltage against current. The result would be a hyperbola in the first quadrant with its concave portion looking upwards; indicating constant power output such that the voltage times the current equals a constant. It is also known that real main generators have voltage/current characteristic curves within the first quadrant with the concave portion facing downwards thereby intersecting the hyperbola of the Diesel engine at two points for the same Diesel engine speed. Regulation systems try to reconcile the two characteristics so as to make best use of the power delivered by the Diesel engine.
Indeed, the aim of regulation is to ensure that at all times, the generator supplies electric power which is always equal to and is never greater than the power supplied by the Diesel engine so that the engine can be used to maximum effect and need never be in a situation where it reaches its upper limit, in which case it would slow down. In conventional regulator systems, self-regulation is used which is based on the fact that when the Diesel engine speed drops, the speed of an auxiliary generator driven by the Diesel engine also drops, thereby causing a reduction in the excitation current and therefore in the power of the main generator. External regulation is also used and is operated by a rheostat which controls and accentuates the reduction in excitation current of the main power unit when the Diesel engine power tends to increase relative to a value fixed as a function of the Diesel engine speed.
The regulation systems used up till now have the disadvantage of taking effect only in the hyperbolic zone Diesel engine characteristic in electric co-ordinates, but not in the substantially rectilinear high-current/lowvoltage or high-voltage/low-current branches disposed on either side of the secant points of the hyperbola and merging with portions of the load curve of the main generator. In other words, prior art regulator systems have the disadvantage of not acting as regulators when starting up a train or when the train is running at high speed.
In prior art regulator systems for Diesel electric locomotives, there is a control handle operated by the driver and which sets a Diesel engine rotation speed. The control "handle" is sometimes a "wheel", but the term "handle" is used for either in this specification. In prior art systems, there is also a Diesel engine power regulator which makes the injection of gas oil vary as a function of a comparison between the measured true rotation speed of the Diesel engine and the value set by the driver, the aim of the increase or decrease of injection being to maintain the required rotation speed at the set constant value. Prior art Diesel engine power regulators use equipment of hydraulic design.
In prior art regulator systems, there is also an excitation regulator for the main generator; said regulator regulates the generators excitation as a function of the Diesel engine speed as measured by means of a tachometer. Its function is to operate in such a way that for a given speed, the power supplied by the main generator is always less than or equal to the power which the Diesel engine can supply.
One prior art system is illustrated by U.S. Pat. No. 3,370,218.
It can be seen from the above that in prior art systems, the disadvantage of regulating the excitation of the main generator as a function of the Diesel engine speed is that it limits Diesel engine power only in a middle zone which corresponds to said hyperbola, since setting the Diesel engine speed leads, in actual fact, to setting the Diesel engine power. The disadvantage of the prior art system is therefore that is does not function in all cases which may occur during operation.
Preferred embodiments of the present invention remedy these drawbacks. Indeed, they allow a choice of parameters which enable the power brought into play at any speed and on starting up the locomotive.